The environment pollutions caused by pollution sources such as industrial boilers, power plant boilers and industrial furnace, or the like are very severe nowadays, and thus countries all over the world are diving to the relevant researches for the purpose of controlling those pollutions. As a result, there is a need of monitoring the concentration of particulate matter emitted by those pollution sources. At present, common monitoring methods include opacity method, light transmission method, laser back-scattering method, triboelectricmethod, and β-ray absorption method (testing inside a flue), etc.
In these methods, filtrating-weighing method is employed most broadly nowadays. The basic principle of this method is: a certain volume dust-containing smoke passes through a filter cylinder with known weight where dust particulates in the smoke are stopped and deposited such that the soot concentration can be calculated according to the weight difference of the filter cylinder before and after sampling and the volume of sampling. Since the smoke in flue has a certain flow rate and pressure as well as a pretty high temperature and humidity, and often contains some erosive gas, an isokinetic sampling method must be employed here. Many nations take filtrating-weighing method as a standard method because of its high accuracy and good precision. Similarly, China also selects this method as the standard of appraising other analysis methods. With reference to FIG. 1, it is a diagram of the internal structure of a β-ray soot concentration direct-reading monitor in the prior art, which comprises: a soot collection unit and a soot mass detection unit, and said soot collection unit comprises a soot sampling gun, a filter paper and a mechanical-control auto filter paper feeding structure, wherein said soot sampling gun includes a gathering tube 11, a Pitot tube and a sheath tube. The soot passing through the gathering tube directly covers on the filter paper 3 and then is analyzed by means of a β-ray source 52.
The Chinese patent numbered 02238238.0 disclosed a β-ray particulates emission continuous monitor, characterizing in that it includes a cantilever sampling tube, a compressor, a filter paper and a filter paper feeding device, a β-ray source (carbon 14 source), a β-ray receiving Geiger-Muller detector, a S Pitot tube, a computer-based data processing device and a casing. The sampling tube of this β-ray particulates emission continuous monitor is connected to a negative pressure source. The filter paper is drawn by the filter paper feeding device to pass through the cross section of the sampling tube, and then pass between the β-ray source and the β-ray receiving GEIGER-MULLER detector. The β-ray receiving GEIGER-MULLER detector is electrically connected with the computer-based data processing device. The S Pitot tube is connected by pipes with the compressor. A temperature sensor also is electrically connected with the computer-based data processing device. With reference to FIG. 2, it is a structural diagram of the soot sampling gun of a β-ray soot concentration direct-reading monitor in the prior art. As depicted in FIG. 2, sampling tube 11 and Pitot tube 12 are respectively housed in two sheath tubes 13′ and 13″. In this design of the monitor, a heating tube 45 and said sampling tube 11 are provided in the same sheath tube 13′ to heat the soot. However, since the heat provided by the heating tube is not uniform, not only the dehumidifying effect is not obvious but also a reflux condensation is easily caused. Thereby, the heating process loses its value.
To sum up, the present available β-ray soot concentration monitor still has following drawbacks which need to be conquered:
in the case where the sampling acreage is equal to the testing acreage, the mass overflow of the sampling acreage is occurred,
the soot is of high humidity and thus effects the detection of the soot mass,
the detection of the soot with high dispersion (wide-spread distribution??) and large particulate is not accurate because the β-rays emitted from the β-ray source (carbon 14 source) are absorbed completely by soot rather than able to penetrate this kind of the soot at all.
In order to overcome the problems above mentioned, the inventor conducted research and experimentation for a long time and achieved the present invention.